## Step-by-Step Solution and Explanation ### **Left Molecule: Which H is Most Acidic?** First, let's identify the structure: The molecule on the left is **cyclopentadiene**. To determine which hydrogen is most acidic, consider: - The acidity of a hydrogen atom increases if the resulting conjugate base is stabilized (often through resonance). - In cyclopentadiene, removing the hydrogen from the position between the two double bonds (the "bridge" carbon) forms a **cyclopentadienyl anion**, which is aromatic (6 π electrons, follows Hückel's rule). **Therefore, the most acidic hydrogen is the one attached to the sp³-hybridized carbon between the two double bonds (the methylene group).** ### **Right Molecule: Which Site is Most Basic?** The molecule on the right is **pyridine** (a six-membered aromatic ring with a nitrogen atom). For basicity: - A basic site is typically a lone pair that can accept a proton. - In pyridine, the nitrogen atom has a lone pair that is **not** involved in the aromatic π system, so it is free to act as a base and accept a proton. **Therefore, the most basic site is the nitrogen atom in the ring.** --- ## **Final Answers** For the left molecule (cyclopentadiene), the most acidic hydrogen is the one on the carbon between the two double bonds (the "methylene" carbon). For the right molecule (pyridine), the most basic site is the nitrogen atom in the aromatic ring.